1. Field of the Invention
The present invention relates to saboted projectiles, more particularly to a plastic sabot, or combination of plastic sabots, supported by a metal or ceramic, or rigid plastic skeleton, which encloses a substantially smaller caliber bullet.
2. Problems in the Art
Fairly recent technology, involving encasing a bullet in a plastic sabot, makes it possible to fire a sub-caliber projectile down a large bore behind large powder charge. The decreased mass of the lighter projectile and sabot provides velocities higher than possible for a full caliber bullet fired down a standard bore size. This allows the use of a smaller and lighter bullet (or projectile) with higher sectional density and ballistic coefficient, providing improved downrange performance and enhancing longer range hit possibilities; it also reduces recoil.
This high-tech sabot application is currently used by not only the military, but also by the muzzle loading sport shooters and shotgun slug hunters. Modern large caliber muzzle loading rifles (shooting saboted bullets) and shotguns (shooting saboted slugs) have advanced to the limit of current technology, with muzzle velocities approximately only half way between large full caliber bullet (or slug) velocity and smaller caliber centerfire cartridge rifle velocity, even with muzzleloaders that use smokeless powder.
Modern muzzle loading rifles and shotgun slug shooters are limited by the amount of caliber reduction in the plain plastic sabot. The plain plastic sabot begins to fail as barrel temperature, caliber difference, or velocity is increased. For example, the normal plastic sabot material used in shotgun shot cups (for slug sabots) and low velocity black powder muzzle loading, fails to maintain accuracy when the barrel temperature rises to any degree, due to failure of bullet (slug) support and gas seal problems. The same problem occurs when velocity is increased or when caliber is reduced to any significant level. The plastic deforms under increased launching pressure, compromising bullet support and gas seal as it travels down the barrel. As the thickness of the sabot plastic wall increases, the potential for plastic deformation and bullet yaw increases. Increasing the stiffness of the plastic has limits in practicality and in function. As the rigidity of the plastic petals enclosing the bullet (slug) increases, problems in sabot disengagement have an adverse affect on accuracy, causing unacceptable accuracy dispersion. This is a main reason centerfire rifle cartridges with high velocity sub-caliber saboted rounds failed to gain acceptance, following their introduction.
Modern muzzleloaders can only be successfully reduced about five calibers (e.g. 50 caliber to 45 caliber), without significantly damaging accuracy, at the present intermediate velocities. This results in mediocre sectional densities and ballistic coefficients; that translates to rapid velocity loss as the bullet or slug travels down range. Mediocre velocity quickly degrades to low velocity with rapid bullet drop and inadequate bullet performance. Increasing the mass and sectional density of the bullet only increases bullet drop and recoil; velocity is decreased, along with downrange performance. It does not decrease terminal bullet performance except on the largest game; this does not make it a good deer hunters choice. Shotgun slugs have similar problems; velocities are even necessarily lower with even greater increases in caliber differences in order to maintain what is often marginal accuracy.
The prior art limitation is a combination of very limited support, combined with gas seal inadequacies, both being antagonized by the problem of need for a clean rapid release, presently afforded by the inadequate plain plastic sabot.
Furthermore, the sabot""s advantages of improved long-range accuracy and velocity come at the expense of easy loading. Tight fitting sabots have to be hammered down into place above the muzzleloader""s powder charge. This is unpopular with the muzzle loading community and there is currently a trend away from the sabot, returning to slightly under full caliber projectile designs reminiscent to those used in the civil war (Minxc3xa9 ball).
There is still a problem with the Minxc3xa9 ball. It is close to full-caliber, the increased mass and decreased sectional density correspondingly cause decreased velocity and decreased downrange performance as well as increased recoil. In addition, the slightly sub-caliber bullet only seals at the base, permitting some yaw or wobble, as the bullet travels down the bore. This adversely affects accuracy. The length of the bullet may be increased to partially overcome this problem; however, this only increase projectile mass even more. The result is further increased recoil and decreased downrange performance.
There are advances in military sabot technology that have addressed the preceding problems to some degree, in the use of armor piercing fin-stabilized discarding sabot ammunition. Typically, they incorporate a brittle shaft rod-type projectile comprised of tungsten or depleted uranium, designed for penetrating armor plate. There are many designs; most are concerned with solid base support and stabilizing the penetrator during launch.
Two designs are most relevant to prior art bullet and sabot discussions. U.S. Patent H001353 by Malejko is a statutory invention, not a patent. It uses a disc away from the base of the sub-caliber projectile, towards the rod-type penetrator nose. This permits a greater amount of propellant in the cartridge, surrounding the rearward projecting sub caliber stabilizing the fins of the sabot. The disc expands to fill full-bore diameter upon firing, forming a gas seal and propelling the saboted projectile down the bore. U.S. Patent H001412 by Kline is also a statutory invention, not a patent. It uses metal stabilizing fins between petals in the plastic sabot, preventing flexing of the rod-type penetrator upon firing, which degrades accuracy.
There is therefore a need to design a sabot that provides sufficient rigidity to prevent bullet flexing in the sabot (eroding accuracy), sufficient flexibility of the sabot to provide a xe2x80x9ccleanxe2x80x9d accuracy-enhancing bullet release, and sufficient bullet solid base and/or forward support that also makes an expandable strong gas seal.
For the muzzle loading community, there is also a need for easier loading of the saboted projectile. It is also desirable to incorporate any means to minimize fouling of powder residue in the barrel between shots, as this increases the difficulty of seating the next projectile on the powder charge.
Features of the Invention
A general feature of the invention is the provision of an improved sabot, which overcomes problems found in the prior art.
A feature of the invention is improved stability in sabot support, which does not have an adverse affect on accuracy of the bullet or slug.
A further feature of the invention is flexible support that permits a clean rapid release of the projectile, so as to permit good accuracy.
An additional feature of the invention is an improved design and function that permits higher velocities for the sabot-supported projectile.
Yet another feature of the invention is the provision of a skeletal framework within the sabot, which provides improved gas seal and support strength, yet does not scar the gun barrel.
Still further feature of the invention is the provision of a flexible plastic soft body portion of the sabot that functions as a stable full-length guide for the projectile down the gun barrel, and yet permits a clean release of the bullet or slug, following exit from the gun barrel.
For further feature of the invention is the possibility of a plastic sabot encased within another plastic sabot, providing a two-stage caliber reduction, with skeletal support.
Another feature is duplicating the easy loading of the Minxc3xa9 ball (in a muzzleloader) using the modifications of the formerly hard-to-load sabot.
Yet still another feature is the self-cleaning action of a gas-check, which minimizes fouling from black powder and other propellants commonly used in muzzleloaders.
These, as well as other features and advantages of the present invention, will become apparent from the following specification and claims.
The invention is directed to a discardable sabot for transporting a sub-caliber projectile, when fired in a chamber, down and out a gun barrel, whereby it is then released. The sabot may be utilized in a muzzle loading capacity, resting on a powder charge in the firing chamber. The sabot may also be utilized in a shotgun shell cartridge or in a traditional centerfire (brass) rifle or pistol cartridge. Vertebrate biomechanics are used as a pattern for the model. The internal skeleton of fishes, amphibians, reptiles, and mammals does a far better job of supporting (strengthening) larger body mass than any invertebrate exoskeleton. At the same time it affords superior agility and soft body function. Some of these attributes are desirable to overcome prior art limitations of sabot construction and function in projectile support.
The sabot skeleton is integrated into an ordinary plain plastic sabot, reinforcing crucial areas. It is comprised of a nearly full-caliber rear-facing concave metal (or ceramic and/or rigid plastic) disc that supports the base of the sub-caliber projectile (bullet). Upon firing, the disc expands to full-caliber, deforming into the rifled bore""s lands and grooves, and acts as a gas seal. This functions much as the Minxc3xa9 ball skirt, at the base of the bullet from the Civil War era, did. It is sufficiently rigid so as to resist further deformation upon firing. The rest of the skeletal support is located inside the plastic sabot""s cavity, contributing to lengthwise rigidity. It is a slightly under caliber metal (or ceramic and/or rigid plastic) ring(s), that may or may not be segmented and may or may not be attached to the base disc. The (segmented) ring may be further sectioned at an angle along the longitudinal axis, dividing the skeletal ring into upper and lower halves. This would allow the upper half of the support ring to slip slightly rearward and laterally upon firing. The skeletal ring surrounds the longitudinal sub-caliber bullet (or slug) much as the segmented sabot petals do, forming a rigid ring (circle) around it; in turn, the sabot""s plastic petals surround the skeletal ring. The forward skeletal ring sections are designed to upset their surrounding plastic sabot petals into the rifling as they slip past the rear ring sections, in a rearward and lateral direction, when the gun is fired. This duplicates the action of the expanding skirt in the rear portion providing support in the base and frontal area. This effectively doubles the Minxc3xa9 ball type of support, greatly enhancing stability as the sabot travels down the bore. The upset, from slightly under the rifled bore""s land diameter, to barrel groove diameter is caused by gas pressure in the barrel from firing, albeit lower in the front of the sabot than it is behind the sabot. The plastic sabot is simply reinforced in the area necessary (while traveling down the barrel) for improved stability. Thin flexible plastic sabot petals are still able to provide a rapid clean release of the bullet upon exit from the barrel. This permits an improved caliber reduction within the sabot. Accuracy in enhanced. Performance downrange is improved. Recoil is lessened.
Two stage sabot systems are possible for even greater caliber reductions. A ring of the stiff skeletal petals could occupy a space between one sabot enclosed within another sabot. The skeletal sabot offers many possibilities and combinations.
An alternate embodiment could support the bullet above a tapered metal disk, with metal fins surrounding the bullet, much as feathers surround the shaft on an arrow. Filling the remaining bulk with hollow plastic sections would reduce weight even further than with the previous embodiments.
Thus the improved skeletal support overcomes the shortcomings of the plain plastic sabot.